Pervaporation membranes and methods of use

Abstract

Pervaporation membranes including poly(acrylamide)-grafted alginate membranes, which may be optimized for the separation of alcohols from water, low viscosity sodium alginate membranes containing PEG and PVA, which may be optimized for the separation of organic acids from water, and copolymeric PAN-grafted PVA membranes, which may be optimized for the separation of DMF from water, and methods of making such membranes. Use of such membranes in pervaporation and pervaporation devices containing such membranes. Use of such membranes alone or in combination with ion-exchange membranes for recovery of organic compounds or for water purification applications such as production of potable water or industrial waste treatment. The membranes of the present invention may be used to remove trace amounts of water from organic compounds.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a process for making pervaporation separation membranes that can be used for the separation of organic substances, particularly volatile organic substances, from water. More particularly, it relates to novel processes for producing and using membranes for the effective separation of alcohols, organic acids and other organic compounds from water and vice versa. The invention additionally includes pervaporation membranes made by the processes of the invention and methods of using such membranes.BACKGROUND OF THE INVENTION[0002]A number of organic compounds may be found in water, particularly water contaminated by various industrial processes. It is desirable to remove such compounds from the water for a large variety of reasons, ranging from water purification to recovery of the organic compounds.[0003]As is well known to those skilled in the art, it is possible to remove water from mixtures thereof with organic liquids by v...

AI Technical Summary

Benefits of technology

[0067]Temperature dependence of pervaporation flux and diffusivity results for the feed mixture containing 20 mass % of water presented in Table V were used to estimate the activation parameters in the Arrhenius equation:

[0068]TABLE VPervaporation Flux and Separation Selectivity atDifferent Temperature for 20 Mass % of Water in the FeedMixture for Different MembranesJp × 102 (kg / m2h) eq. (3)αsep, eq. (4)Temp.NaAlg-NaAlg-NaAlg-NaAlg-(° C.)NaAlg12NaAlg123013.815.117.296.096.053.14019.118.119.768.760.043.15025.920.521.955.353.130.8

[0069]The driving force for mass transport, which represents the concentration gradient resulting from the difference in partial vapor pressure of permeants between the feed and the permeate, increases with increasing temperature. As the feed temperature increases, the vapor pressure in the feed compartment also increases, but the vapor pressure at the permeate side is not affected resulting in increase of driving force at higher temperatures. The apparent activation energy data for permeation, Ep calculated from the slopes of the straight lines of the Arrhenius plots using the least squares method are presented in Table VI. The Ep values vary according to the sequence: NaAlg>NaAlg-1>NaAlg-2.

[0070]TABLE VIPermeation and Diffusion Activation Energies, Heatof Sorption of Water and Energy Difference Values of theMembranesParametersNaAlgNaAlg-1NaAlg-2EP (kJ / mol) eq. (6)5.601.59.84ED (kJ / mol) eq. (7)7.074.052.38ΔHS (kJ / mol)1.492.472.54EISO-OH − EW (kJ / mol)6.634.242.16

[0071]Similarly, results of mass transport due to activated diffusion are described by the equation:

[0072]The temperature dependency of αsep was investigated using the relationship described in Ping, Z. H.; Nguyen, Q. T.; Clement, R.; Neel, J. J Membr Sci 1990, 48, 297, which is as follows:

Problems solved by technology

These conventional processes, particularly distillation, are however, characterized by high capital cost.

In the case of distillation, for example, the process requires expensive distillation towers, heaters, heat exchangers (reboilers, condensers, etc), together with a substantial amount of auxiliary equipment typified by pumps, collection vessels, vacuum generating equipment, etc.

Such operations are characterized by high operating costs principally costs of heating and cooling-plus pumping, etc.

Furthermore, the properties of the materials being separated, as is evidenced by the distillation curves, may be such that a large number of plates may be required, etc.

When the material forms an azeotrope with water, additional problems may be present which for example, would require that separation be effected in a series of steps (e.g. as in two towers) or by addition of extraneous materials to the system.

There are also comparable problems which are unique to adsorption systems.

However, sodium alginate membranes suffer from lack of mechanical stability.

However, even sodium alginate membranes with these improvements in mechanical stability remain unsuitable for many uses.

In addition to addressing mechanical stability problems, achieving the simultaneous enhancement of both selectivity and flux or enhancement of one characteristic without decrease of the other is a challenging task in the area of pervaporation membranes.

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